Constant velocity universal joint

ABSTRACT

The constant velocity universal joint comprises an outer joint member  1  that has three curved guide grooves  1   b  formed in the axial direction on a spherical inner circumferential surface  1   a  thereof, an inner joint member  2  that has three curved guide grooves  2   b  formed in the axial direction on a spherical outer circumferential surface  2   a  thereof, three torque transmitting balls  3  disposed in ball tracks that are formed by the coordination of the guide grooves  1   b  of the outer joint member  1  and the guide grooves  2   b  of the inner joint member  2 , a cage  4  that holds the balls  3 , and elastic pressing means  5  interposed between the outer circumferential surface  2   a  of the inner joint member  2  and the inner circumferential surface  4   a  of the cage  4.

BACKGROUND OF THE INVENTION

The present invention relates to a constant velocity universal jointthat is suited to applications where rotation backlash is undesirable,and is particularly preferable for the steering apparatus of anautomobile.

In the steering apparatus of an automobile, for example as shownschematically in FIG. 34, rotation torque imparted to a steering wheel20 is transmitted via a main shaft 21 of a steering column and anintermediate shaft 22 to a gear shaft (pinion shaft or the like) 24 of asteering gear 23, while being converted to a linear motion by themechanism of the steering gear 23 thereby to be transmitted via a linkmechanism (knuckle or the like) 25 to wheels 26 as steering force. Thesteering gear 23 may be one of various types including rack and piniontype, ball screw type and worm roller type, while the rack and piniontype is predominantly used for the reason of high rigidity and lightweight thereof. The intermediate shaft 22 is disposed at an angle to themain shaft 21 and the gear shaft 24, and is connected to the main shaft21 and the gear shaft 24 via universal joints 27, 28, for the purpose ofabsorbing the impact energy in case of collision.

While the Cardan joint (universal joint employing cross yokes) has beenpredominantly used for the universal joints (27, 28) of the steeringapparatus, constant velocity universal joints are being increasinglyemployed instead of the Cardan joint in order to allow a larger angle inthe joint (in conjunction with the layout of vehicle components) andimprove the movement of the joint (feel of the steering operation).

Meanwhile a constant velocity universal joint of ordinary constitutionhas a small clearance (inner gap) between torque transmitting ball and aball track, which inevitably results in rotation backlash (play in thecircumferential direction) taking place in the joint when the directionof rotation changes. Thus use of the constant velocity universal jointof the ordinary constitution in the steering apparatus leads to suchproblems as the loss of stability in steering, and loss of sharp ordirect feel of steering.

In the field of automobile, constant velocity universal joints have manyrecords of applications to the drive shaft, and the constant velocityuniversal joint of the ordinary constitution is normally designed tosuch specifications that satisfy the requirements of the drive shaft. Inthe case of the steering apparatus, however, since less load torque isapplied to the joint and the joint rotates at lower speeds than thedrive shaft, the constant velocity universal joint of the ordinaryconstitution has rather excessively higher specifications compared tothe required characteristics, and therefore improvements are requiredfor the reduction of joint weight and manufacturing cost.

The ball fixed type constant velocity universal joint of this type alsorequires the complicated assembly process as described above, andtherefore has such disadvantages as follows.

(1) The assembly work requires skilled technique and is difficult tomechanize (automate).

(2) It is necessary to make the guide grooves of the inner and outerjoint members longer (in the axial direction) than the length requiredfor the function, in order to facilitate the assembly of the balls, thusresulting in larger joint dimension.

(3) It is necessary to make the size of the pocket of the cage in thecircumferential direction larger, in order to facilitate the assembly ofthe balls (because the balls move in the circumferential direction inthe pocket of the cage when the inner and outer joint members are causedto make angular displacement). This makes a disadvantage in the designof the cage in terms of strength.

(4) It is necessary to prepare the inner joint member and the shaftseparately (in case the inner joint member and the shaft are prepared asan integral part, the shaft interferes with the outer joint member whenassembling the balls, thus making it impossible to secure the amount ofangular displacement required for the assembly). This leads to increasesin the number of parts and in the number of assembly steps.

SUMMARY OF THE INVENTION

An object of the present invention is to solve the problem of rotationbacklash in the ball fixed type constant velocity universal joint, andprovide a simpler, light weight, compact and low-cost ball fixed typeconstant velocity universal joint that can be assembled in an improvedprocess.

Another object of the present invention is to ensure good feel ofrotation (smoothness of rotation) and, when applied to the steeringapparatus in particular, improve the performance such as the feel ofsteering, while maintaining the constant velocity characteristics ofthis type of constant velocity universal joint.

Yet another object of the present invention is to reduce the resistanceto the rotation in the constant velocity universal joint of this typeand ensure good feel of rotation (smoothness of rotation) and, when usedin a steering apparatus in particular, improve the performance such asthe steering force, auto-centering of the steering wheel and the feel ofsteering.

In order to achieve the objects described above, the present inventionprovides a ball fixed type constant velocity universal joint comprisingan outer joint member having a curved guide groove formed in the axialdirection on a spherical inner circumferential surface thereof, an innerjoint member having a curved guide groove formed in the axial directionon a spherical outer circumferential surface thereof, ball disposed in aball track formed by the coordination of the guide groove of the outerjoint member and the guide groove of the inner joint member, and a cagethat holds the ball, with the center of the guide groove of the outerjoint member and the center of the guide groove of the inner jointmember being offset to the opposite sides to each other by equaldistances in the axial direction with respect to the center plane of thejoint that include the centers of the ball, the ball track beinggradually reduced toward the opening or the innermost side of the joint,wherein the inner joint member is allowed to make relative displacementin the axial direction with respect to the cage, and elastic pressingmeans having a spherical surface that makes fitting contact with theouter circumferential surface of the inner joint member is interposedbetween the outer circumferential surface of the inner joint member andthe inner circumferential surface of the cage, so that the elastic forceof the elastic pressing means presses the outer circumferential surfaceof the inner joint member toward the side opposite to the offsetdirection of center of the guide groove thereof.

The inner joint member makes a relative displacement in the axialdirection opposite to the offset direction under the urging pressure ofthe elastic pressing means, thereby to press the ball, and stops at aposition where the inner gap between the balls and the guide grooves ofthe inner and outer joint members disappears. As a result, a certainamount of preload is applied in the axial direction to the ball, thuseliminating the rotation backlash (play in the circumferentialdirection). Also because the spherical surface of the elastic pressingmeans presses the outer circumferential surface of the inner jointmember, the surface pressure in the portion of contact between bothmembers is reduced and the outer circumferential surface of the innerjoint member can be guided by the spherical surface.

In the constitution described above, the ball track may have such aconfiguration that is gradually reduced toward the opening side of thejoint, at least the region on the opening side of the innercircumferential surface of the cage is a cylindrical surface that fitswith the outer circumferential surface of the inner joint member, andthe elastic pressing means is disposed on the cylindrical surface. Thisconfiguration makes it possible to assemble the inner joint member intothe inner circumferential surface of the cage after assembling the cageand the ball into the outer joint member.

In addition to the constitution described above, the region on theopening side of the inner circumferential surface of the outer jointmember may have a cylindrical surface that fits with the outercircumferential surface of the cage. This configuration makes it easierto assemble the cage into the outer joint member.

Since the inner joint member can be assembled after assembling the cageand the balls in the outer joint member, it is made possible tointegrate the inner joint member and the shaft (to form in an integralpart, or bond together) thereby decreasing the number of parts and thenumber of assembly steps, without causing any trouble in the assemblyoperation.

Further, in order to achieve the objects described above, the presentinvention provides a ball fixed type constant velocity universal jointcomprising an outer joint member having a curved guide groove formed inthe axial direction on a spherical inner circumferential surfacethereof, an inner joint member having a curved guide groove formed inthe axial direction on a spherical outer circumferential surfacethereof, ball disposed in ball track formed by the coordination of theguide groove of the outer joint member and the guide groove of the innerjoint member, and a cage that holds the ball, with the center of theguide groove of the outer joint member and the center of the guidegroove of the inner joint member being offset to the opposite sides toeach other by equal distances in the axial direction with respect to thecenter plane of the joint that includes the center of the ball, the balltrack being gradually reduced toward the opening or the innermost sideof the joint, wherein at least the region on the opening side of theinner circumferential surface of the cage is formed in a cylindricalsurface that fits the outer circumferential surface of the inner jointmember, and a retaining member having a spherical portion that makesfitting contact with the outer circumferential surface of the innerjoint member is disposed on the cylindrical surface. This type constantvelocity universal joint can be used for a connection joint for driveshafts, propeller shafts or the like of automobile, in addition tosteering apparatus.

This configuration makes it possible to assemble the inner joint memberinto the inner circumferential surface of the cage after assembling thecage and the ball into the outer joint member, by forming at least theregion on the opening side of the inner circumferential surface of thecage in a cylindrical surface that fits the outer circumferentialsurface of the inner joint member. After being assembled in the innercircumferential surface of the cage, the inner joint member is retainedin place by the retaining member that is disposed on the cylindricalsurface of the cage. The outer circumferential surface of the innerjoint member is guided by the spherical portion of the retaining member.

In addition to the constitution described above, the region on theopening side of the inner circumferential surface of the outer jointmember may also be formed in a cylindrical surface that fits the outercircumferential surface of the cage. This configuration makes it easierto assemble the cage into the outer joint member.

Since the inner joint member can be assembled after assembling the cageand the ball in the outer joint member, it is made possible to integratethe inner joint member and the shaft (to form in an integral part, orbond together) thereby decreasing the number of parts and the number ofassembly steps, without causing any trouble in the assembling operation.

Also, in order to achieve the objects described above, the presentinvention provides a constant velocity universal joint comprising anouter joint member having a curved guide groove formed in the axialdirection on a spherical inner circumferential surface thereof, theguide groove having center of curvature at a point (O1) that is offsetby a predetermined distance (f1) from the center of curvature of thespherical inner circumferential surface to one side in the axialdirection, an inner joint member having a curved guide groove formed inthe axial direction on a spherical outer circumferential surfacethereof, the guide groove having center of curvature at a point (O2)that is offset by a predetermined distance (f2) from the center ofcurvature of the spherical outer circumferential surface to the otherside in the axial direction, a ball track formed by the coordination ofthe guide groove of the outer joint member and the guide groove of theinner joint member that opposes the former, the ball track havingwedge-like shape that reduces toward the other side in the axialdirection, torque transmitting ball disposed in the ball track, a cagethat holds the torque transmitting ball, and preloading means thatreduces a clearance between the torque transmitting balls and the balltrack by causing an elastic relative displacement to take place in theaxial direction between at least one of the outer joint member and theinner joint member and the torque transmitting ball, wherein the offsetdistance (f1) of the center of curvature (O1) of the guide groove of theouter joint member and the offset distance (f2) of the center ofcurvature (O2) of the guide groove of the inner joint member are set tohave different values, and such a configuration is employed as thecenter of curvature (O1) and the center of curvature (O2) are offset tothe opposite sides by the same distances (f) in the axial direction withrespect to the center plane of the joint that includes the center of thetorque transmitting ball, when the clearance is reduced by thepreloading means.

Specific embodiments of the preloading means may be, for example, (1) tohave the torque transmitting ball undergo a displacement in the axialdirection toward the reduced side of the ball track, (2) to have theinner joint member undergo a displacement in the axial directionopposite to the offset direction of the center of curvature of the guidegroove thereof, (3) to have the outer joint member undergo adisplacement in the axial direction to the offset direction of thecenter of curvature of the guide groove thereof, or (4) to have theinner joint member undergo a displacement in the axial directionopposite to the offset direction of the center of curvature of the guidegroove thereof and to have the outer joint member undergo a displacementin the axial direction to the offset direction of the center ofcurvature of the guide groove thereof.

Relation of inequality and difference between the offset distance (f1)of the center of curvature (O1) of the guide groove of the outer jointmember and the offset distance (f2) of the center of curvature (O2) ofthe guide groove of the inner joint member are set by taking intoconsideration the mode of preloading, the amount of inner gap (theamount of rotation backlash: play in the circumferential direction),presence and size of clearance between the torque transmitting ball andthe cage and other factors, so that the center of curvature (O1) and thecenter of curvature (O2) are offset to the opposite sides by the samedistances (f) in the axial direction with respect to the center plane ofthe joint that includes the center of the torque transmitting ball whenthe clearance is reduced by the preloading means. This makes it possibleto achieve good feel of rotation (smoothness of rotation) whilemaintaining the constant velocity characteristics of the joint. Relationbetween the offset distance (f1) and the offset distance (f2) may be setto satisfy f1>f2, or to satisfy f1<f2.

The preloading means may be constituted from, for example, a clearanceprovided in the axial direction between the inner joint member and thecage, and an elastic member that is interposed between the inner jointmember and the cage and presses the inner joint member in a directionopposite to the offset direction of the center of the guide groove ofthe inner joint member. In this case, under the pressing force of theelastic member applied thereto, the inner joint member makes a relativedisplacement in the axial direction opposite to the offset direction ofthe center of curvature of the guide groove thereby to press the torquetransmitting ball, and stops at a position where the inner gap betweenthe torque transmitting balls and the guide groove (ball track) of theinner and outer joint members disappears. As a result, a certain amountof preload is applied in the axial direction to the torque transmittingball, thus eliminating the rotation backlash (play in thecircumferential direction).

Regions that are free of undercut may be provided in the guide groovesof the outer joint member and the inner joint member. This makes itpossible to increase the operating angle of the joint.

The region on the opening side of the inner circumferential surface ofthe outer joint member may be formed in a cylindrical surface that fitswith the outer circumferential surface of the cage. This makes it easierto assemble the cage into the outer joint member.

The constant velocity universal joint of the present invention is lightin weight, small in size and low cost, and rotates smoothly withoutbacklash while being capable of taking a large operating angle, and istherefore particularly preferable for the steering apparatus of anautomobile.

Also, in order to solve the problems described above, the presentinvention provides a constant velocity universal joint comprising anouter joint member having a curved guide groove formed in the axialdirection on a spherical inner circumferential surface thereof, an innerjoint member having a curved guide groove formed in the axial directionon a spherical outer circumferential surface thereof, a ball trackformed by the coordination of the guide groove of the outer joint memberand the guide groove of the inner joint member that opposes the former,the ball track having wedge-like shape that reduces toward one side inthe axial direction, torque transmitting ball disposed in the balltrack, a cage having a pocket that holds the torque transmitting ball,and preloading means that reduces the clearance between the torquetransmitting balls and the ball track, wherein the clearance δ of thepocket in the axial direction between the pocket of the cage and thetorque transmitting ball is set in a range of 0≦δ≦55 μm.

The reason for setting the clearance δ of the pocket in the axialdirection in the range of 0≦δ≦55 μm is as follows. In the constantvelocity universal joint of this type (ball fixed type constant velocityuniversal joint), the clearance δ of the pocket in the axial directionis normally set to be δ<0 (negative clearance) thereby allowing a slighttightening allowance between the pocket of the cage and the torquetransmitting ball, in view of the importance placed on the function ofthe cage to guide the torque transmitting ball (function to keep thetorque transmitting ball in the bisecting plane (θ/2) of the operatingangle θ, thereby to ensure constant velocity characteristic of thejoint). However, since setting the clearance δ of the pocket in theaxial direction to a negative value makes it difficult for the torquetransmitting ball to roll over the ball track, this setting has adisadvantage in terms of the resistance to rotation (torque) when thejoint of this type transmits rotation torque while taking an operationangle. Resistance of the joint to rotation affects the performance suchas the steering force and auto-centering capability in a steeringapparatus, and is preferably as small as possible. Although rollingperformance of the torque transmitting balls can be improved therebydecreasing the resistance of the joint to rotation by setting theclearance δ of the pocket in the axial direction to be δ≧0 (positiveclearance), making the clearance δ of the pocket in the axial directiontoo large leads to a decrease in the capability of the cage to guide thetorque transmitting ball, resulting in the loss of the constant velocitycharacteristic of the joint. In the steering apparatus, loss of theconstant velocity characteristic of the joint leads to the generation ofunusual sound and deterioration in the feel of steering such as hitch.Therefore, it is necessary to set the clearance δ of the pocket in theaxial direction in an optimum range in order to reduce the resistance ofthe joint to rotation and achieve good feel of steering (smoothness ofrotation).

Accordingly, a test was conducted to determine the optimum range of theclearance δ of the pocket in the axial direction. The results are shownin Table 1. The test was conducted on the constant velocity universaljoint of this embodiment shown in FIG. 1 and FIG. 2. Sample jointshaving different sizes of clearance δ of the pocket (δ=L−D_(BALL): referto FIG. 6) in the axial direction were fabricated and tested to evaluatethe resistance to rotation and the feel of steering (smoothness ofrotation) under a predetermined operating angle θ and a predeterminedmagnitude of rotation torque applied thereto. The resistance to rotationwas evaluated by whether it was greater or smaller than a criterion. Thefeel of steering was rated as ◯ when a criterion was exceeded, Δ whenthe criterion was missed with a little margin and ▴ when the criterioncould not be reached with a large margin. Comprehensive evaluation whichcombined the resistance to rotation and the reel of steering was ratedas ◯ when the total criterion was reached or Δ when not.

TABLE 1 Clearance δ of the pocket in the axial direction (μm) −20 0 +20+55 +80 Resistance to Greater Smaller Smaller Smaller Smaller rotationFeel of Δ ◯ ◯ ◯ ▴ steering Comprehensive Δ ◯ ◯ ◯ Δ evaluation

As will be apparent from the test results, satisfactory performance wasachieved in both the resistance to rotation and the feel of steeringwhen the clearance δ of the pocket in the axial direction was set in arange of 0≦δ≦55μm. When δ<0, resistance of the joint to rotationincreases because it becomes difficult for the torque transmitting ballsto roll. When δ>55 μm, on the other hand, the joint cannot operate withsatisfactory constant velocity characteristic, thus resulting in poorerfeel of steering with such impression as hitch. In view of reducing theresistance of the joint to rotation and achieving good feel of steering(smoothness of rotation) while maintaining the constant velocitycharacteristic, the optimum range for the clearance δ of the pocket inthe axial direction is 0≦δ≦55 μm.

The preloading means reduces the inner clearance provided between thetorque transmitting ball and the ball track by causing a relativedisplacement between any two components among the outer joint member,the inner joint member, the cage and the torque transmitting ball. Thepreloading means may be constituted from, for example, a clearanceprovided in the axial direction between the inner joint member and thecage, and an elastic member that is interposed between the inner jointmember and the cage and presses the inner joint member in a directionopposite to the offset direction of the center of the guide groove ofthe inner joint member. In this case, under the pressing force of theelastic member applied thereto, the inner joint member makes a relativedisplacement in the axial direction opposite to the offset direction ofthe guide groove thereby to press the torque transmitting ball, andstops at a position where the inner clearance between the torquetransmitting ball and the guide grooves (ball track) of the inner andouter joint members disappears. As a result, a certain amount of preloadis applied in the axial direction to the torque transmitting balls, thuseliminating the rotation backlash (play in the circumferentialdirection).

Regions that are free of undercut may be provided in the guide groovesof the outer joint member and the inner joint member. This makes itpossible to increase the operating angle of the joint.

The region on the opening side of the inner circumferential surface ofthe outer joint member may be formed in a cylindrical surface that fitswith the outer circumferential surface of the cage. This makes it easierto assemble the cage into the outer joint member.

The constant velocity universal joint of the present invention is lightin weight, small in size and low cost, and rotates smoothly withoutbacklash with less resistance to rotation, while being capable of takinga large operating angle, and is therefore particularly preferable forthe steering apparatus of an automobile.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a cross sectional view (FIG. 1a) illustrating firstembodiment of the present invention and a longitudinal sectional view(FIG. 1b) taken along line b—b in FIG. 1a.

FIG. 2 is an enlarged longitudinal sectional view of portion X in FIG.1.

FIG. 3 is a longitudinal sectional view showing an outer joint member.

FIG. 4 is a longitudinal sectional view showing an inner joint member.

FIG. 5 shows a longitudinal sectional view (FIG. 5a) of a cage and arightward view (FIG. 5b) of FIG. 5a.

FIG. 6 shows a front view (FIG. 6a) of elastic pressing means and asectional view (FIG. 6b) taken along line b—b in FIG. 6a.

FIG. 7A illustrates a step of assembling a cage into the innercircumferential surface of the outer joint member in a process ofassembling the constant velocity universal joint according to apreferred embodiment;

FIG. 7B illustrates a step of assembling the ball into the pocket of thecage in the process of assembling the constant velocity universal joint;

FIG. 7C illustrates a step of assembling the inner joint member into theinner circumferential surface of the cage, assembling the elasticpressing device into the inner circumferential surface of the cage, andsecuring the elastic pressure device with a retainer ring in the processof assembling the constant velocity universal joint; and

FIG. 7D illustrates the fully assembling joint.

FIG. 8 is a partially enlarged longitudinal sectional view inmodification of the first embodiment.

FIG. 9 shows a cross sectional view (FIG. 9a) illustrating secondembodiment of the present invention and a longitudinal sectional view(FIG. 9b) taken along line b—b in FIG. 9a.

FIG. 10 is an enlarged longitudinal sectional view of portion X in FIG.9.

FIG. 11 is a longitudinal sectional view showing an outer joint member.

FIG. 12 is a longitudinal sectional view showing an inner joint member.

FIG. 13 shows a longitudinal sectional view (FIG. 12a) of a cage and arightward view (FIG. 13b) of FIG. 13a.

FIG. 14 shows a front view (FIG. 14a) of a retaining member and asectional view (FIG. 14b) taken along line b—b in FIG. 14a.

FIG. 15A illustrates a step of assembling a cage into the innercircumferential surface of the outer joint member in a process ofassembling the constant velocity universal joint according to a secondembodiment;

FIG. 15B illustrates a step of assembling the ball into the pocket ofthe cage in the process of assembling the constant velocity universaljoint;

FIG. 15C illustrates a step of assembling the inner joint member intothe inner circumferential surface of the cage, assembling the elasticpressing device into the inner circumferential surface of the cage, andsecuring the elastic pressure device with a retainer ring in the processof assembling the constant velocity universal joint; and

FIG. 15D illustrates the fully assembled joint.

FIG. 16 is a longitudinal sectional view of the constant velocityuniversal joint of third embodiment.

FIG. 17 is a cross sectional view taken along line O—O in FIG. 16 (bootis omitted).

FIG. 18 is an enlarged longitudinal sectional view of a key portion inFIG. 1.

FIG. 19 is a longitudinal sectional view (partially side view) of theouter joint member.

FIG. 20 is a longitudinal sectional view (partially side view) of theinner joint member.

FIG. 21 shows a longitudinal sectional view (FIG. 21a) of the cage and arightward view (FIG. 21b) of FIG. 21a.

FIG. 22 shows a front view (FIG. 22a) of the elastic member and asectional view (FIG. 22b) taken along line b—b in FIG. 22a.

FIG. 23 is an enlarged sectional view of a key portion of the constantvelocity universal joint according to modification of the thirdembodiment.

FIG. 24 is an enlarged sectional view of a key portion of the constantvelocity universal joint according to another modification of the thirdembodiment.

FIG. 25 is a longitudinal sectional view of the constant velocityuniversal joint of forth embodiment.

FIG. 26 is a cross sectional view taken along line O—O in FIG. 25 (bootis omitted).

FIG. 27 is an enlarged longitudinal sectional view of a key portion inFIG. 25.

FIG. 28 is a longitudinal sectional view (partially side view) of theouter joint member.

FIG. 29 is a longitudinal sectional view (partially side view) of theinner joint member.

FIG. 30 shows a longitudinal sectional view (FIG. 30a) of the cage and arightward view (FIG. 30b) of FIG. 30a.

FIG. 31 shows a front view (FIG. 31a) of the elastic member and asectional view (FIG. 31b) taken along line b—b in FIG. 31a.

FIG. 32 is an enlarged sectional view of a key portion of the constantvelocity universal joint according to modification of the forthembodiment.

FIG. 33 is an enlarged sectional view of a key portion of the constantvelocity universal joint according to another modification of the forthembodiment.

FIG. 34 shows schematically an example of the automobile steeringapparatus.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now preferred embodiments of the present invention will be describedbelow with reference to the accompanying drawings.

As shown in FIG. 1, the constant velocity universal joint of thisembodiment comprises an outer joint member 1 that has, for example,three curved guide grooves 1 b formed in the axial direction on aspherical inner circumferential surface 1 a thereof, an inner jointmember 2 that has, for example, three curved guide grooves 2 b formed inthe axial direction on a spherical outer circumferential surface 2 athereof, for example, three balls 3 disposed in ball tracks that areformed by the coordination of the guide grooves 1 b of the outer jointmember 1 and the guide grooves 2 b of the inner joint member 2, a cage 4that holds the balls 3, and elastic pressing means 5 interposed betweenthe outer circumferential surface 2 a of the inner joint member 2 andthe inner circumferential surface 4 a of the cage 4.

As shown in FIG. 3, the outer joint member 1 has a cup shape that opensat one end thereof and is provided with either a shaft formed integrallytherewith at the other end not shown or a separate shaft being bonded byproper means. Center A of the guide groove 1 b is offset by apredetermined distance in the axial direction (toward the innermost sideof the joint in this embodiment) with respect to the center of curvatureO of the inner circumferential surface 1 a. A region on the opening sideof the inner circumferential surface 1 a is formed in a cylindricalsurface 1 a 1. Inner radius D1 of the cylindrical surface 1 a 1 is madeequal to or larger than the radius D4 (refer to FIG. 5) of the outercircumferential surface 4 c of the cage 4 (D1≧D4).

In this embodiment, as shown in FIG. 4, the inner joint member 2 and theshaft 2 c are formed as an integral part. This configuration is chosento decrease the number of parts and the number of assembly steps. CenterB of the guide groove 2 b is offset by a predetermined distance in theaxial direction (toward the opening side of the joint in thisembodiment) with respect to the center of curvature O of the outercircumferential surface 2 a. The offset distance of the guide groove 2 bis the same as the offset distance of the guide groove 1 b of the outerjoint member 1, but opposite in direction (the guide groove 1 b beingoffset toward the innermost side, and the guide groove 2 b being offsettoward the opening side).

In this embodiment, as shown in FIG. 5, the cage 4 has three window-likepockets 4 b that accommodate the balls 3. The inner circumferentialsurface 4 a of the cage 4 has a region on the opening side formed in acylindrical surface 4 a 1 and an inner region formed in a conicalsurface 4 a 2. Inner radius D5 of the cylindrical surface 4 a 1 is madeequal to or larger than the outer radius D2 of the outer circumferentialsurface 2 a of the inner joint member 2 (D5≧D2). The innermost regionmay also be a spherical surface or a cylindrical surface. The outercircumferential surface 4 c of the cage 4 is a spherical surface (centerof curvature at O) having radius D4. The cage 4 may be made of a metal,but may also be made of a resin in order to reduce the weight and cost.

In this embodiment, as the elastic pressing means 5 a split ring thatcan freely contract and expand as shown in FIG. 6 is adopted. Theelastic pressing means 5 is made of spring steel or the like, and has anopening 5 a and three claws 5 b that protrude in the axial direction.End of each of the claws 5 b is formed in a concave spherical surface 5c having the same radius of curvature as that of the outercircumferential surface 2 a of the inner joint member 2. The elasticpressing means 5 may also be made of an elastic material such as aresin, a rubber or the like.

FIGS. 7A-D show the process of assembling the constant velocityuniversal joint of this embodiment. The assembling process comprises astep of assembling the cage 4 into the inner circumferential surface 1 aof the outer joint member 1 (step a as shown in FIG. 7A), a step ofassembling the balls 3 into the pocket 4 b of the cage 4 (step b asshown in FIG. 7B), a step of assembling the inner joint member 2 intothe inner circumferential surface 4 a of the cage 4, assembling theelastic pressing means 5 into the inner circumferential surface 4 a ofthe cage 4 (cylindrical surface 4 a 1) and securing the elastic pressingmeans with a retainer ring 6 to prevent coming off thereof (step c asshown in FIG. 7C) resulting in the fully assembled joint (step d asshown in FIG. 7D).

In the assembling step a, since the opening side region of the innercircumferential surface 1 a of the outer joint member 1 is thecylindrical surface 1 a 1 having radius D1 (≧D4), the cage 4 can beassembled into the outer joint member 1 by advancing in the axialdirection with the axis of the cage 4 being aligned with the axis of theouter joint member 1. As a result, it is made easier to assemble thecage 4 compared to the case of the prior art process.

In the assembling step b, the balls 3 can be assembled into the pocket 4b directly from the inner circumferential side of the cage 4. As aresult, it is made easier to assemble the balls 3 compared to the priorart process. Also because it is not necessary to make an angulardisplacement of the inner joint member 2 and the cage 4 with respect tothe outer joint member 1 when assembling the balls 3, it is madepossible to make the dimensions in the axial direction of the guidegrooves 1 b, 2 b of the inner and outer joint members 1, 2 and thedimension of the pocket 4 b of the cage 4 in the circumferentialdirection thereof smaller than those of the prior art. Consequently, thejoint can be made lighter in weight and smaller in size, and thestrength thereof (strength of cage) can be improved.

In the assembling step c, since the opening side region of the innercircumferential surface 4 a of the cage 4 is the cylindrical surface 4 a1 having radius D5 (≧D2) and the center B of the guide groove 2 b of theinner joint member 2 is offset toward the opening side, the inner jointmember 2 can be assembled into the inner circumferential surface 4 a ofthe cage 4 and the balls 3 by advancing the inner joint member 2 in theaxial direction under such a state that the axis of the inner jointmember 2 is aligned with the axes of the cage 4 and the outer jointmember 1. Thus it is made easier to assemble the inner joint member 2than in the case of prior art process. Also because the inner jointmember 2 can be assembled after assembling the cage 4 and the balls 3into the outer joint member 1, thus integrating the shaft 2 c with theinner joint member 2 does not cause any difficulty in assembling.

In the assembling step d, the elastic pressing means 5 is assembled intothe inner circumferential surface 4 a (cylindrical surface 4 a 1) of thecage 4, and the outer circumferential surface 2 a of the inner pointmember is pressed toward the innermost side in the axial direction bythe spherical surface 5 c, with the retainer ring 6 applied to preventthe elastic pressing means 5 from coming off. Instead of using theretainer ring 6, the elastic pressing means 5 may also be secured toprevent it from coming off by such means as caulking the elasticpressing means 5 onto the cylindrical surface 4 a 1 of the cage 4,bonding (welding, etc.) and fitting engagement (for example, aprojection provided on the elastic pressing means 5 is fitted in anengagement groove formed in the cylindrical surface 4 a 1 of the cage4).

When the outer joint member 1, the inner joint member 2, the balls 3,the cage 4, and the elastic pressing means 5 have been assembled in theconfiguration described above, the constant velocity universal joint ofthis embodiment shown in FIG. 1 is completed. Center A of the guidegroove 1 b of the outer joint member 1 and center B of the guide groove2 b of the inner joint member 2 are offset on the opposite sides to eachother (center A is offset toward the innermost side of the joint andcenter B is offset toward the opening of the joint) in the axialdirection by the same distances with respect to the center plane O ofthe joint that includes the centers of the balls 3. Thus the ball trackformed by the coordination of the guide groove 1 b and the guide groove2 b has a wedge shape that expands toward the innermost side andgradually reduces toward the opening side.

As shown in FIG. 2 (enlarged view of portion X of FIG. 1), a clearance Sis formed in the axial direction between the inner circumferentialsurface 4 a of the cage 4 (conical surface 4 a 2) and the outercircumferential surface 2 a of the inner joint member 2, thereby toallow a relative displacement of the inner joint member 2 in the axialdirection with respect to the cage 4. The outer circumferential surface2 a of the inner joint member 2 is pressed to the side (innermost side)opposite to the offset direction (toward the opening) of center B of theguide groove 2 b by the elastic force F of the elastic pressing means 5that is interposed between the outer circumferential surface 2 a of theinner joint member 2 and the inner circumferential surface 4 a of thecage 4 (cylindrical surface 4 a 1). Under the elastic force F of theelastic pressing means 5, the inner joint member 2 makes a relativedisplacement in the axial direction opposite to the offset direction(innermost side) thereby to press the balls 3 and stops at a positionwhere the inner gap between the balls 3 and the guide grooves 1 b, 2 bof the inner and outer joint members 1, 2 disappears. As a result, acertain amount of preload F is applied in the axial direction to theballs 3, thus eliminating the rotation backlash (play in thecircumferential direction).

While the split ring is used as the elastic pressing means 5, anintegral ring having a shape similar to that shown in FIG. 6 may also beused as long as a sufficient elastic force can be obtained. In thiscase, the elastic force required may be exerted by the elasticity ofclaws or a separate elastic ring 5″ that complements the elasticity ofclaws 5 b′of the integral ring 5′ as shown in FIG. 8 may be provided.The elastic ring 5″ is, for example, a corrugated plate spring, a rubberring or a resin ring. The elastic ring 5″ may also be used together withthe split ring 5 shown in FIG. 6. or, alternatively, the elastic ring 5″may also be used together with a rigid ring (a ring which is notelastic) that makes contact with the outer circumferential surface 2 aof the inner joint member 2. In this case, the elastic pressing means ofthe present invention consists of the combination of a pressing member(a member which is not elastic) that presses the outer circumferentialsurface of the inner joint member and an elastic member that applies anelastic force to the former member. The elastic pressing means of thepresent invention is not limited to ring shape and may be made of anymaterial in any shape as long as the object of the present invention canbe achieved.

By the first embodiment, the following effects can be obtained.

(1) The inner joint member makes a relative displacement in the axialdirection opposite to the offset direction under the predeterminedurging pressure of the elastic pressing means, thereby to press theballs, and applies a certain amount of preload in the axial direction tothe balls. This eliminates the rotation backlash (play in thecircumferential direction) of the joint. Also because the elasticpressing means has the spherical surface that fits and makes contactwith the outer circumferential surface of the inner joint member, thesurface pressure in the portion of contact between the outercircumferential surface of the inner joint member and the elasticpressing means is reduced and the outer circumferential surface of theinner joint member can be guided by the spherical surface.

(2) By making the ball track in such a configuration that is graduallyreduced toward the opening side of the joint, and forming thecylindrical surface that fits with the outer circumferential surface ofthe inner joint member at least in the region on the opening side of theinner circumferential surface of the cage with the elastic. pressingmeans being disposed on the cylindrical surface, it is made possible toassemble the inner joint member easily. Also because the inner jointmember can be assembled after assembling the cage and the balls into theouter joint member, the inner joint member and the shaft can beintegrated thereby reducing the number of parts and the number ofassembling steps.

(3) Since it is not necessary to make an angular displacement of theinner joint member and the cage with respect to the outer joint memberwhen assembling the balls, dimension of the guide grooves of the innerand outer joint members in the axial direction can be made smaller thanthose in the prior art and the size in the circumferential direction ofthe pocket of the cage can be made smaller than those in the prior art.Thus the joint can be made lighter in weight and smaller in size, andthe strength (strength of cage) can be increased.

(4) By forming the region on the opening side of the innercircumferential surface of the outer joint member in cylindrical surfacethat fits with the outer circumferential surface of the cage, it is madeeasier to assemble the cage into the outer joint member.

As shown in FIG. 9, the constant velocity universal joint of secondembodiment comprises an outer joint member 1 that has, for example,three curved guide grooves 1 b formed in the axial direction on aspherical inner circumferential surface 1 a thereof, an inner jointmember 2 that has, for example, three curved guide grooves 2 b formed inthe axial direction on a spherical outer circumferential surface 2 athereof, for example, three balls 3 disposed in ball tracks that areformed by the coordination of the guide grooves 1 b of the outer jointmember 1 and the guide grooves 2 b of the inner joint member 2, a cage 4that holds the balls 3, and a retaining member 5 interposed between theouter circumferential surface 2 a of the inner joint member 2 and theinner circumferential surface 4 a of the cage 4.

As shown in FIG. 11, the outer joint member 1 has a cup shape that opensat one end thereof and is provided with either a shaft formed integrallytherewith at the other end not shown or a separate shaft being bondedthereto by proper means. Center A of the guide groove 1 b is offset by apredetermined distance in the axial direction (toward the innermost sideof the joint in this embodiment) with respect to the center of curvatureO of the inner circumferential surface 1 a. A region on the opening sideof the inner circumferential surface 1 a is formed in a cylindricalsurface 1 a 1. Inner radius D1 of the cylindrical surface 1 a 1 is setto such a value that is capable of enclosing the profile of the cage 4shown in FIG. 13(a) in conjunction with a recess of the guide groove 1 bof the outer joint member 1.

In this embodiment, as shown in FIG. 12, the inner joint member 2 andthe shaft 2 c are formed as an integral part. This configuration ischosen to decrease the number of parts and the number of assembly steps.Center B of the guide groove 2 b is offset by a predetermined distancein the axial direction (toward the opening side of the joint in thisembodiment) with respect to the center of curvature O of the outercircumferential surface 2 a. The offset distance of the guide groove 2 bis the same as the offset distance of the guide groove 1 b of the outerjoint member 1, but is opposite in direction (the guide groove 1 b beingoffset toward the innermost side, and the guide groove 2 b being offsettoward the opening side).

In this embodiment, as shown in FIG. 13, the cage 4 has threewindow-like pockets 4 b that accommodate the balls 3. The innercircumferential surface 4 a of the cage 4 has a region on the openingside which is formed in a cylindrical surface 4 a 1 and an innermostside region which is formed in a spherical surface 4 a 2 (center ofcurvature at O). Inner radius D5 of the cylindrical surface 4 a 1 ismade equal to or larger than the outer radius D2 of the outercircumferential surface 2 a of the inner joint member 2 (D5≧D2). Theinnermost side region may also be formed in a conical surface or acylindrical surface. The outer circumferential surface 4 c of the cage 4is a spherical surface (center of curvature at O) having radius D4. Thecage 4 may be made of a metal, but may also be made of a resin in orderto further reduce the weight and cost.

In this embodiment, a ring as shown in FIG. 14 is adopted as theretaining member 5. The retaining member 5 is made of steel or the like,and has three claws 5 b that protrude in the axial direction. End ofeach of the claws 5 b is formed in a concave spherical surface 5 chaving the same radius of curvature as that of the outer circumferentialsurface 2 a of the inner joint member 2. The retaining member 5 may alsobe made of a resin or the like.

FIGS. 15A-D show the process of assembling the constant velocityuniversal joint of this embodiment. The assembling process comprises astep of assembling the cage into the inner circumferential surface 1 aof the outer joint member 1 (step a as shown in FIG. 15A), a step ofassembling the balls 3 into the pocket 4 b of the cage 4 (step b asshown in FIG. 15B), a step of assembling the inner joint member 2 intothe inner circumferential surface 4 a of the cage 4, assembling theretaining member 5 into the inner circumferential surface 4 a(cylindrical surface 4 a 1) of the cage 4 and securing with a retainerring 6 to prevent the assembly from coming off (step c as shown in FIG.15C) resulting in the fully assembled joint (step d as shown in FIG.15D).

In the assembling step a, since the opening side region of the innercircumferential surface 1 a of the outer joint member 1 has thecylindrical surface 1 a 1 that can enclose the profile of the cage 4shown in FIG. 13(a), the cage 4 can be assembled into the outer jointmember 1.

In the assembling step b, the balls 3 can be assembled into the pocket 4b directly from the inner circumferential side of the cage 4. As aresult, it is made easier to assemble the balls 3 compared to the priorart process. Also because it is not necessary to make an angulardisplacement of the inner joint member 2 and the cage 4 with respect tothe outer joint member 1 when assembling the balls 3, it is madepossible to make the dimensions in the axial direction of the guidegrooves 1 b, 2 b of the inner and outer joint members 1, 2 smaller thanthose of the prior art and make the dimension of the pocket 4 b of thecage 4 in the circumferential direction thereof smaller than that of theprior art. Consequently, the joint can be made lighter in weight andsmaller in size, and the strength thereof (strength of cage) can beincreased.

In the assembling step c, since the opening side region of the innercircumferential surface 4 a of the cage 4 has the cylindrical surface 4a 1 having radius D5 (≧D2) and the center B of the guide groove 2 b ofthe inner joint member 2 is offset toward the opening side, thus theinner joint member 2 can be assembled into the inner circumferentialsurface 4 a of the cage 4 and the balls 3 by advancing the inner jointmember 2 in the axial direction under such a state that the axis of theinner joint member 2 is aligned with the axes of the cage 4 and theouter joint member 1. Thus it is made easier to assemble the inner jointmember 2 than in the case of the prior art process. Also because theinner joint member 2 can be assembled after assembling the cage 4 andthe balls 3 into the outer joint member 1, thus integrating the shaft 2c with the inner joint member 2 does not cause any difficulty inassembling.

In the assembling step d, the retaining member 5 is assembled into theinner circumferential surface 4 a (cylindrical surface 4 a 1) of thecage 4, and the spherical portion 5 c thereof is fitted with the outercircumferential surface 2 a of the inner joint member 2, with theretainer ring 6 applied to prevent the assembly from coming off. Insteadof using the retainer ring 6, the retaining member 5 may also be securedto prevent it from coming off by such means as caulking the retainingmember 5 onto the cylindrical surface 4 a 1 of the cage 4, bonding(welding, etc.) and fitting engagement (for example, a projectionprovided on the retaining member 5 is fitted in an engagement grooveformed in the cylindrical surface 4 a 1 of the cage 4).

When the outer joint member 1, the inner joint member 2, the balls 3,the cage 4, and the retaining member 5 have been assembled in theconfiguration described above, the constant velocity universal joint ofthis embodiment shown in FIG. 9 is completed. Center A of the guidegroove 1 b of the outer joint member 1 and center B of the guide groove2 b of the inner joint member 2 are offset on the opposite sides to eachother (center A is offset toward the innermost side of the joint andcenter B is offset toward the opening of the joint) in the axialdirection by the same distances with respect to the center plane O ofthe joint that includes the centers of the balls 3. Thus the ball tracksformed by the coordination of the guide grooves 1 b and the guidegrooves 2 b has a wedge shape that expands toward the innermost side andgradually reduces toward the opening.

As shown in FIG. 10 (enlarged view of portion X of FIG. 9), the innerjoint member 2 assembled into the inner circumferential surface 4 a ofthe cage 4 is retained and held in place by the retaining member 5. Theouter circumferential surface 2 a of the inner joint member 2 is guidedby the spherical surface 4 a 2 of the cage 4 and the spherical portion 5c of the retaining member 5 during angular displacement of the joint.

While an integral ring is used as the retaining member in thisembodiment, a split ring (split at one position or at a plurality ofpositions) having a shape similar to that shown in FIG. 14 may also beused as long as the required force of retention can be obtained. Theretaining member may also be pressed toward the inner joint member by anelastic member such as a corrugated plate spring, a rubber ring or aresin ring. Moreover, the retaining member of the present invention isnot limited to a ring shape and may be made of any material in any shapeas long as the object of the present invention can be achieved.

By the second embodiment, the following effects can be obtained.

(1) The inner joint member can be assembled more easily by providing thecylindrical surface, that fits the outer circumferential surface of theinner joint member, in at least the opening side region of the innercircumferential surface of the cage, and disposing the retaining memberon the cylindrical surface. Also because the inner joint member can beassembled after assembling the cage and the balls into the outer jointmember, it is made possible to integrate the shaft with the inner jointmember and reduce the number of parts and the number of assembly steps.Further, because the retaining member has the spherical surface thatmakes fitting contact with the outer circumferential surface of theinner joint member, the outer circumferential surface of the inner jointmember can be guided by the spherical surface.

(2) Since it is not necessary to make an angular displacement of theinner joint member and the cage with respect to the outer joint memberwhen assembling the balls, dimensions of the guide grooves of the innerand outer joint members in the axial direction can be made smaller thanthose in the prior art and the size in the circumferential direction ofthe pocket of the cage can be made smaller than that in the prior art.Thus the joint can be made lighter in weight and smaller in size, andthe strength (strength of cage) can be increased.

(3) By forming the region on the opening side of the innercircumferential surface of the outer joint member in a cylindricalsurface that fits with the outer circumferential surface of the cage, itis made easier to assemble the cage into the outer joint member.

The constant velocity universal joint of third embodiment shown in FIG.16 and FIG. 17 connects an intermediate shaft (22) and a gear shaft (24)of a steering gear (23) to be capable of freely making angulardisplacement in, for example, an automobile steering apparatus shown inFIG. 34.

The constant velocity universal joint of this embodiment comprises anouter joint member 1 that has, for example, three curved guide grooves 1b formed in the axial direction on a spherical inner circumferentialsurface 1 a thereof, an inner joint member 2 that has, for example,three curved guide grooves 2 b formed in the axial direction on aspherical outer circumferential surface 2 a thereof, for example, threetorque transmitting balls 3 disposed in ball tracks that are formed bythe coordination of the guide grooves 1 b of the outer joint member 1and the guide grooves 2 b of the inner joint member 2 that oppose theformer, a cage 4 that holds the torque transmitting balls 3, and anelastic member 5 interposed between the outer circumferential surface 2a of the inner joint member 2 and the inner circumferential surface 4 aof the cage 4.

As shown in FIG. 19, the outer joint member 1 of this embodiment has acup shape that opens at one end thereof and is provided with a yoke 1 cformed integrally therewith at the other end thereof for connecting agear shaft (for example, a pinion shaft) of a steering gear (forexample, a rack and pinion type steering gear). By integrally formingthe outer joint member 1 and the yoke 1 c, it is made possible to reducethe number of manufacturing processes, the number of parts and thenumber of assembly steps and reduce the cost. concentricity of bothmembers can also be ensured.

The center of curvature O1 of the guide groove 1 b is offset by thepredetermined distance f1 from the center of curvature O1′ of thespherical inner circumferential surface 1 a to one side (toward theinnermost side of the joint in this embodiment) in the axial direction.A region on the opening side of the inner circumferential surface 1 a isformed in a cylindrical surface 1 a 1. Inner radius D1 of thecylindrical surface 1 a 1 is set to such a value that is capable ofenclosing the outer diameter of the cage 4 (direction shown in FIG.21(a)) to be described later.

The outer joint member 1 is preformed roughly to a predetermined shapefrom steel in hot forging or semi-hot forging process, while the innercircumferential surface 1 a and the guide groove 1 b are formed in coldforging process. While the inner circumferential surface 1 a is furthersubjected to a post process (grinding process or the like) to ensureaccuracy, the cold forging process described above may be regarded asthe final finishing process for the guide groove 1 b. In this case,surface of the guide groove 1 b constitutes the surface of the finalproduct that has been formed by cold forging. Since this makes the postprocessing (grinding, etc.) of the guide groove unnecessary,manufacturing cost for the outer joint member is reduced in comparisonto the prior art.

In this embodiment, as shown in FIG. 20, the inner joint member 2 hasthe shaft 2 c that serves also as the intermediate shaft (22: refer toFIG. 34) being integrally formed therewith. Forming the shaft 2 cintegrally with the inner joint member 2 makes it possible to reduce thenumber of manufacturing processes, the number of parts and the number ofassembly steps and reduce the cost.

The center of curvature O2 of the guide groove 2 b is offset by apredetermined distance f2 from the center of curvature O2′ of thespherical outer circumferential surface 2 a to the other side (towardthe opening of the joint in this embodiment) in the axial direction.Direction of offset of the guide groove 2 b is opposite to that of theguide groove 1 b of the outer joint member 1 (the guide groove 1 b isoffset toward the innermost side, and the guide groove 2 b is offsettoward the opening). In this embodiment, the offset distance f2 of theguide groove 2 b is set to be smaller than the offset distance f1 of theguide groove 1 b of the outer joint member 1 by a predetermined amount(f1>f2).

The inner joint member 2 is preformed roughly to a predetermined shapefrom steel in, for example, hot forging or semi-hot forging process,while the outer circumferential surface 2 a and the guide groove 2 b areformed in cold forging process. While the outer circumferential surface2 a is subjected to a post process (grinding process or the like) toensure accuracy, the cold forging process described above may beregarded as the final finishing process for the guide groove 2 b. Inthis case, surface of the guide groove 2 b makes the surface of thefinal product that has been formed by cold forging. Since this makes thepost processing (grinding, etc.) of the guide groove unnecessary,manufacturing cost of the inner joint member is reduced in comparison tothe prior art.

In this embodiment, as shown in FIG. 21, the cage 4 has threewindow-like pockets 4 b that accommodate the torque transmitting balls3. The inner circumferential surface 4 a of the cage 4 has a region onthe opening side that is formed in a cylindrical surface 4 a 1 and aninnermost side region formed in a conical surface 4 a 2. Inner radius D5of the cylindrical surface 4 a 1 is made larger than the outer radius D2of the outer circumferential surface 2 a of the inner joint member 2(D5>D2). The innermost side region may also be formed in a sphericalsurface or a cylindrical surface. The outer circumferential surface 4 cof the cage 4 is a spherical surface having radius D4. The cage 4 may bemade of a metal, but may also be made of a resin in order to furtherreduce the weight and cost.

In this embodiment, dimension L in the axial direction of the pocket 4 bof the cage 4 is equal to or greater than diameter D_(BALL) of thetorque transmitting balls 3 accommodated therein (L≧D_(BALL)). Clearanceδ (=L−D_(BALL)) of the pocket in the axial direction between the pocket4 b and the torque transmitting balls 3 may be set, for example, in arange of 0≦δ≦55μm. This setting makes it possible to reduce theresistance to the rotation when the joint transmits the rotation torquewhile taking a certain operating angle and prevent the joint from losingthe constant velocity characteristics, thereby to achieve good feel ofrotation (smoothness of rotation).

In this embodiment, a split ring that can increase and decrease thediameter thereof as shown in FIG. 22 is adopted as the elastic member 5.The elastic member 5 is made of spring steel or the like, and has oneopening 5 a and three claws 5 b that protrude in the axial direction.End of each of the claws 5 b is formed in a concave spherical surface 5c having the same radius of curvature as that of the outercircumferential surface 2 a of the inner joint member 2. The elasticmember 5 may also be made of an elastic material such as resin orrubber. The elastic member 5 may also be made in an integral ringwithout the split gap 5 a. In this case, the elastic force required maybe provided by the elasticity of the claws (5 b), or by the combined useof an elastic ring such as a corrugated plate spring, a rubber ring or aresin ring. Further, the end portion (5 c) of the claw (5 b) may beformed in such a shape that makes linear contact with the outercircumferential surface 2 a of the inner joint member 2, for example aconical shape (conical surface).

The constant velocity universal joint of this embodiment is assembledthrough a step of assembling the cage 4 into the inner circumferentialsurface 1 a of the outer joint member 1, a step of assembling the torquetransmitting balls 3 into the pocket 4 b of the cage 4, a step ofassembling the inner joint member 2 into the inner circumferentialsurface 4 a of the cage 4, and a step of assembling the elastic member 5into the inner circumferential surface 4 a (cylindrical surface 4 a 1)of the cage 4 and securing with a retainer ring 6 to prevent theassembly from coming off. Since the region on the opening side of theinner circumferential surface 1 a of the outer joint member 1 has thecylindrical surface 1 a 1 that can enclose the profile of the cage 4(direction shown in FIG. 21(a)), the cage 4 can be easily assembled intothe outer joint member 1. Also the torque transmitting balls 3 can beassembled into the pocket 4 b directly from the inner circumferentialside of the cage 4. Moreover, since the region on the opening side ofthe inner circumferential surface 4 a of the cage 4 has the cylindricalsurface 4 a 1 having radius D5 (>D2) and the center of curvature O2 ofthe guide groove 2 b of the inner joint member 2 is offset toward theopening side, the inner joint member 2 can be assembled into the innercircumferential surface 4 a of the cage 4 and the torque transmittingballs 3 by advancing the inner joint member 2 in the axial directionunder such a state that the axis of the inner joint member 2 is alignedwith the axes of the cage 4 and the outer joint member 1. The elasticmember 5 is assembled into the inner circumferential surface 4 a(cylindrical surface 4 a 1) of the cage 4, and the outer circumferentialsurface 2 a of the inner joint member 2 is pressed toward the inside ofthe joint in the axial direction by the spherical portion (or conicalportion) 5 c of the elastic member 5, with the retainer ring 6 appliedfor retention. Instead of using the retainer ring 6, the elastic member5 may also be secured to prevent it from coming off by such means ascaulking the elastic member 5 onto the cylindrical surface 4 a 1 of thecage 4, bonding (welding, etc.) and fitting engagement (for example, aprojection provided on the elastic member 5 is fitted in an engagementgroove formed in the cylindrical surface 4 a 1 of the cage 4).

When the outer joint member 1, the inner joint member 2, the torquetransmitting balls 3, the cage 4, and the elastic member 5 have beenassembled in the configuration described above, the constant velocityuniversal joint of this embodiment shown in FIG. 16 and FIG. 17 iscompleted. A boot 10 is applied on the outer circumference of the outerjoint member 1 and on the outer circumference of the shaft 2 c of theinner joint member 2, and is clamped by means of boot bands 11, 12.

As shown in an enlarged view of FIG. 18, a clearance S is provided inthe axial direction between the inner circumferential surface 4 a(conical surface 4 a 2) of the cage 4 and the outer circumferentialsurface 2 a of the inner joint member 2, thereby to allow a relativedisplacement of the inner joint member 2 in the axial direction withrespect to the cage 4 (and the outer joint member 1). The axialclearance S and the elastic member 5 constitute the preloading means.

Elastic force E of the elastic member 5, that is interposed between theouter circumferential surface 2 a of the inner joint member 2 and theinner circumferential surface 4 a (cylindrical surface 4 a 1) of thecage 4, presses the outer circumferential surface 2 a of the inner jointmember 2 in the direction (toward the innermost side of the joint)opposite to the direction (toward the opening of the joint) of offset ofthe center of curvature O2 of the guide groove 2 b. Under the pressingforce E of the elastic member 5, the inner joint member 2 undergoes arelative displacement in the axial direction in the direction (towardthe innermost side of the joint) opposite to the direction of offset ofthe center of curvature O2, thereby to press the torque transmittingballs 3, and stops at a position where the clearance between the torquetransmitting balls 3 and the guide grooves 1 b, 2 b of the outer andinner joint members 1, 2 disappears. As a result, a certain amount ofpreload E is applied in the axial direction to the torque transmittingballs 3, thus eliminating the rotation backlash (play in thecircumferential direction).

In this embodiment, as described previously, the offset distance f1(offset with respect to the center of curvature O1′) of the guide groove1 b of the outer joint member 1 is set to be larger than the offsetdistance f2 (offset with respect to the center of curvature O2′) of theguide groove 2 b of the inner joint member 2 by a predetermined amount(f1>f2). Consequently, in the state after assembly shown in FIG. 16(state where the inner clearance is reduced by the preloading means),center of curvature O1 of the guide groove 1 b of the outer joint member1 and center of curvature O2 of the guide groove 2 b of the inner jointmember 2 are offset on the opposite sides to each other (center ofcurvature O1 is offset toward the innermost side of the joint and centerof curvature O2 is offset toward the opening of the joint) in the axialdirection by the same distances f with respect to the center plane O ofthe joint that includes the centers O3 of the torque transmitting balls3. Specifically, assuming the state before the clearance is reduced bythe preloading means, the torque transmitting balls 3 have apredetermined amount of play (inner clearance) toward the expanding sideof the ball track, namely in the direction of offset of the center ofcurvature O1 (direction of approaching the center of curvature O1:direction in which the offset distance f1 apparently decreases) withrespect to the guide groove 1 b, and in the direction opposite to theoffset of the center of curvature O2 (direction of departing from thecenter of curvature O2: direction in which the offset distance f2apparently increases) with respect to the guide groove 2 b, takingreference to a position where the balls make contact with both the guidegroove 1 b and the guide groove 2 b (position where there is no innerclearance). Therefore, by setting the offset distance f1 larger than theoffset distance f2 by a predetermined amount (f1>f2), it is madepossible to cancel the variations of the center of curvature O1 and/orthe center of curvature O2 with respect to the center plane O of thejoint in the preloading process so that, when the inner clearance isreduced by the preloading means, the center of curvature O1 and thecenter of curvature O2 are offset to the opposite sides by the samedistances f in the axial direction with respect to the center plane O ofthe joint. Thus the ball tracks formed by the coordination of the guidegrooves 1 b and the guide grooves 2 b are formed in a wedge shape thatgradually reduces toward the other side (opening side) in the axialdirection. When the outer joint member 1 and the inner joint member 2make an angular displacement of θ, the torque transmitting balls 3 whichare guided by the cage 4 are always held in the bisecting plane (θ/2) ofthe angle θ regardless of the value of the operating angle θ. As aresult, constant velocity characteristics of the joint can be ensuredand good feel of rotation (smoothness of rotation) is achieved.

FIG. 23 shows a modification of the third embodiment. In thisembodiment, the guide grooves 1 b of the outer joint member 1 and theguide grooves 2 b of the inner joint member 2 have regions 1 b 1, 2 b 1that are free of undercut being provided thereon. For example, theregion 1 b 1 is provided in the joint on the innermost side of thecenter line O1 of the guide groove 1 b and is parallel to the centerline of the outer joint member 1. The region 2 b 1 is provided in thejoint on the opening side of the center line O2 of the guide groove 2 band is parallel to the center line of the inner joint member 2. Byproviding the regions 1 b 1, 2 b 1 that are free of undercut, theoperating angle of the joint can be increased.

FIG. 24 shows another modification of the third embodiment of thepresent invention. In this embodiment, the entire region of the innercircumferential surface 4 a of the cage 4 is formed in a cylindricalsurface, and the elastic member 5 is mounted in the opening side region4 a 1 of the inner circumferential surface 4 a while an auxiliary ring 7is mounted in the innermost side region 4 a 2 of the innercircumferential surface 4 a. The auxiliary ring 7 is, for example, anintegral ring that has claws 7 b and spherical portions (or conicalportions) 7 c similarly to the elastic member 5 described previously,and is fitted in the innermost side region 4 a 2′ and fastened by aretainer ring 8. The clearance S is provided in the axial directionbetween the spherical surface (or conical surface) 7 c of the auxiliaryring 7 and the outer circumferential surface 2 a of the inner jointmember 2. The clearance S of the axial direction and the elastic member5 constitute the preloading means. This constitution has an advantagethat the configuration of the cage 4 can be mode simpler than in theembodiment described above.

In the automotive steering apparatus shown in FIG. 34, a constantvelocity universal joint similar to that of the embodiments describedabove may be used as a universal joint (28) that connects the main shaft(21) and the intermediate shaft (22) while allowing it to make angulardisplacement freely.

By the third embodiment, the following effects can be obtained.

(1) Since the preloading means is provided to reduce the clearancebetween the torque transmitting balls and the ball track, rotationbacklash (play in the circumferential direction) does not take place.

(2) When the clearance is reduced by the preloading means, the center ofcurvature of the guide groove of the outer joint member and the centerof curvature of the guide groove of the inner joint member are offset onthe opposite sides to each other in the axial direction by the samedistances with respect to the center plane of the joint that includesthe centers of the torque transmitting balls, and consequently constantvelocity characteristics of the joint is maintained and good feel ofrotation (smoothness of rotation) can be achieved.

(3) The operating angle of the joint can be increased by providing theregions free of undercut in the guide grooves of the outer joint memberand the inner joint member.

(4) It is made easier to assemble the cage into the outer joint memberby forming the region on the opening side of the inner circumferentialsurface of the outer joint member in a cylindrical surface that fitsonto the outer circumferential surface of the cage.

(5) The constant velocity universal joint of the present invention islight in weight, small in size and low cost, and rotates smoothlywithout backlash while being capable of taking a large operating angle,and therefore contributes to the improvements in performance such as thestability of steering and feel of steering and in the freedom ofdesigning the layout of vehicle components when used in the steeringapparatus of automobile.

The constant velocity universal joint of forth embodiment shown in FIG.25 and FIG. 26 connects an intermediate shaft (22) and a gear shaft (24)of a steering gear (23) to be capable of freely making an angulardisplacement in, for example, an automobile steering apparatus shown inFIG. 34.

The constant velocity universal joint of this embodiment comprises anouter joint member 1 that has, for example, three curved guide grooves 1b formed in the axial direction on a spherical inner circumferentialsurface 1 a thereof, an inner joint member 2 that has, for example,three curved guide grooves 2 b formed in the axial direction on aspherical outer circumferential surface 2 a thereof, for example, threetorque transmitting balls 3 disposed in ball tracks that are formed bythe coordination of the guide grooves 1 b of the outer joint member 1and the guide grooves 2 b of the inner joint member 2 that oppose theformer, a cage 4 that holds the torque transmitting balls 3 and anelastic member 5 interposed between the outer circumferential surface 2a of the inner joint member 2 and the inner circumferential surface 4 aof the cage 4.

In this embodiment, as shown in FIG. 28, the outer joint member 1 has acup shape that opens at one end thereof and is provided with a yoke 1 cformed integrally therewith at the other end thereof for connecting agear shaft (for example, a pinion shaft) of a steering gear (forexample, a rack and pinion type steering gear). By integrally formingthe outer joint member 1 and the yoke 1 c, it is made possible to reducethe number of manufacturing processes, the number of parts and thenumber of assembly steps and reduce the cost. Concentricity of bothmembers can also be ensured.

The center of curvature O1 of the guide groove 1 b is offset by apredetermined distance f1 from the center of curvature O1′ of the innercircumferential surface 1 a in the axial direction (toward the innermostside of the joint in this embodiment). A region on the opening side ofthe inner circumferential surface 1 a is formed in a cylindrical surface1 a 1. Inner radius D1 of the cylindrical surface 1 a 1 is set to such avalue that is capable of enclosing the outer diameter of the cage 4(direction shown in FIG. 30(a)) to be described later.

The outer joint member 1 is preformed roughly to a predetermined shapefrom, for example, steel in hot forging or semi-hot forging process,while the inner circumferential surface 1 a and the guide groove 1 b areformed in cold forging process. While the inner circumferential surface1 a is further subjected to a post process (grinding or the like) toensure accuracy, the cold forging process described above may beregarded as the final finishing process with regards to the guide groove1 b. In this case, surface of the guide groove 1 b constitutes thesurface of the final product that has been formed by cold forging. Sincethis makes the post processing (grinding, etc.) of the guide grooveunnecessary, manufacturing cost for the outer joint member is reduced incomparison to the prior art.

In this embodiment, as shown in FIG. 29, the inner joint member 2 hasthe shaft portion 2 c that serves also as the intermediate shaft (22:refer to FIG. 34) being integrally formed therewith. Formed on one end(not shown) of the shaft portion 2 c is, for example, a connectingportion that is connected to the outer joint member (having the yokeintegrally formed therewith) of the constant velocity universal joint(having the same constitution as that of the constant velocity universaljoint according to the present embodiment) on the steering wheel side(connected to the yoke). Forming the shaft portion 2 c integrally withthe inner joint member 2 makes it possible to reduce the number ofmanufacturing processes, the number of parts and the number of assemblysteps and reduce the cost.

The center of curvature O2 of the guide groove 2 b is offset by apredetermined distance f2 from the center of curvature O2′ of the outercircumferential surface 2 a in the axial direction (toward the openingside of the joint in this embodiment). Direction of offset of the guidegroove 2 b is opposite to that of the guide groove 1 b of the outerjoint member 1 (the guide groove 1 b is offset toward the innermostside, and the guide groove 2 b is offset toward the opening).

The inner joint member 2 is preformed roughly to a predetermined shapefrom, for example, steel in hot forging or semi-hot forging process,while the outer circumferential surface 2 a and the guide groove 2 b areformed in cold forging process. While the outer circumferential surface2 a is subjected to a post process (grinding process or the like) toensure accuracy, the cold forging process described above may beregarded as the final finishing process for the guide groove 2 b. Inthis case, surface of the guide groove 2 b constitutes the surface ofthe final product that has been formed by cold forging. Since this makesthe post processing (grinding, etc.) of the guide groove unnecessary,manufacturing cost of the inner joint member is reduced in comparison tothe prior art.

In this embodiment, as shown in FIG. 30, the cage 4 has threewindow-like pockets 4 b that accommodate the torque transmitting balls3. The inner circumferential surface 4 a of the cage 4 has a region onthe opening side that is formed in a cylindrical surface 4 a 1 and aninnermost side region formed in a conical surface 4 a 2. Inner radius D5of the cylindrical surface 4 a 1 is made larger than the radius D2 ofthe outer circumferential surface 2 a of the inner joint member 2(D5>D2). The inner region may also be formed in a spherical surface or acylindrical surface. The outer circumferential surface 4 c of the cage 4is a spherical surface having radius D4. The cage 4 may be made of ametal, but may also be made of a resin in order to further reduce theweight and cost.

The dimension L in the axial direction of the pocket 4 b of the cage 4is equal to or greater than diameter D_(BALL) of the torque transmittingballs 3 accommodated therein (L≧D_(BALL)). Clearance δ of the pocket(=L−D_(BALL)) in the axial direction between the pocket 4 b and thetorque transmitting balls 3 is set in a range of 0≦δ≦55μm for the reasondescribed previously.

In this embodiment, a split ring that can increase and decrease thediameter thereof as shown in FIG. 31 is adopted as the elastic member 5.The elastic member 5 is made of spring steel or the like, and has oneopening 5 a and three claws 5 b that protrude in the axial direction.End of each of the claws 5 b is formed in a concave spherical surface 5c having the same radius of curvature as that of the outercircumferential surface 2 a of the inner joint member 2. The elasticmember 5 may also be made of an elastic material such as resin orrubber. The elastic member 5 may also be made in an integral ringwithout the opening 5 a. In this case, the elastic force required may beprovided by the elasticity of the claws (5 b), or by the combined use ofan elastic ring such as a corrugated plate spring, a rubber ring or aresin ring. Further, the end portion (5 c) of the claw (5 b) may beformed in such a shape that makes linear contact with the outercircumferential surface 2 a of the inner joint member 2, for example aconical shape (conical surface).

The constant velocity universal joint of this embodiment is assembledthrough a step of assembling the cage 4 into the inner circumferentialsurface 1 a of the outer joint member 1, a step of assembling the torquetransmitting balls 3 into the pocket 4 b of the cage 4, a step ofassembling the inner joint member 2 into the inner circumferentialsurface 4 a of the cage 4, and a step of assembling the elastic member 5into the inner circumferential surface 4 a (cylindrical surface 4 a 1)of the cage 4 and securing with a retainer ring 6 to prevent theassembly from coming off. Since the region on the opening side of theinner circumferential surface 1 a of the outer joint member 1 has thecylindrical surface 1 a 1 that can enclose the outer diameter of thecage 4 (direction shown in FIG. 30(a)), the cage 4 can be easilyassembled into the outer joint member 1. Also the torque transmittingballs 3 can be assembled into the pocket 4 b directly from the innercircumferential side of the cage 4. Moreover, since the region on theopening side of the inner circumferential surface 4 a of the cage 4 hasthe cylindrical surface 4 a 1 having radius D5 (>D2) and the center O2of the guide groove 2 b of the inner joint member 2 is offset toward theopening side, the inner joint member 2 can be assembled into the innercircumferential surface 4 a of the cage 4 and the torque transmittingballs 3 by advancing the inner joint member 2 in the axial directionunder such a state that the axis of the inner joint member 2 is alignedwith the center axes of the cage 4 and the outer joint member 1. Theelastic member 5 is assembled into the inner circumferential surface 4 a(cylindrical surface 4 a 1) of the cage 4, and the outer circumferentialsurface 2 a of the inner joint member 2 is pressed toward the innermostside of the joint in the axial direction by the spherical portion (orconical portion) 5 c of the elastic member 5, with the retainer ring 6applied for retention. Instead of using the retainer ring 6, the elasticmember 5 may also be secured to prevent it from coming off by such meansas caulking the elastic member 5 onto the cylindrical surface 4 a 1 ofthe cage 4, bonding (welding, etc.) and fitting engagement (for example,a projection provided on the elastic member 5 is fitted in an engagementgroove formed in the cylindrical surface 4 a 1 of the cage 4).

When the outer joint member 1, the inner joint member 2, the torquetransmitting balls 3, the cage 4, and the elastic member 5 have beenassembled in the configuration described above, the constant velocityuniversal joint of this embodiment shown in FIG. 25 and FIG. 26 iscompleted. The center O1 of the guide groove 1 b of the outer jointmember 1 and center O2 of the guide groove 2 b of the inner joint member2 are offset on the opposite sides to each other (center O1 is offsettoward the inside of the joint, and center O2 is offset toward theopening of the joint) in the axial direction by the same distances fwith respect to the center plane O of the joint that includes thecenters O3 of the torque transmitting balls 3. Thus the ball trackformed by the coordination of the guide groove 1 b and the guide groove2 b has a wedge-like shape that expands toward the innermost side andgradually reduces toward the opening. A boot 10 is applied on the outercircumference of the outer joint member 1 and on the outer circumferenceof the shaft 2 c of the inner joint member 2, and is clamped by means ofboot bands 11, 12.

When the outer joint member 1 and the inner joint member 2 make anangular displacement of θ, the torque transmitting balls 3 which areguided by the cage 4 are always held in the bisecting plane (θ/2) of theangle θ regardless of the value of the operating angle θ, therebymaintaining constant velocity characteristics of the joint.

As shown in an enlarged view of FIG. 27, a clearance S is provided inthe axial direction between the inner circumferential surface 4 a(conical surface 4 a 2) of the cage 4 and the outer circumferentialsurface 2 a of the inner joint member 2, thereby to allow a relativedisplacement of the inner joint member 2 in the axial direction withrespect to the cage 4 (and the outer joint member 1). The axialclearance S and the elastic member 5 constitute the preloading means.

Elastic force E of the elastic member 5, that is interposed between theouter circumferential surface 2 a of the inner joint member 2 and theinner circumferential surface 4 a (cylindrical surface 4 a 1) of thecage 4, presses the outer circumferential surface 2 a of the inner jointmember 2 in the direction (toward the innermost side of the joint)opposite to the direction (toward the opening of the joint) of offset ofthe center O2 of the guide groove 2 b. Under the pressing force E of theelastic member 5, the inner joint member 2 undergoes a relativedisplacement in the axial direction to the side (toward the innermostside of the joint) opposite to the direction of offset of the center O2,thereby to press the torque transmitting balls 3, and stops at aposition where the inner clearance between the torque transmitting balls3 and the guide grooves 1 b, 2 b of the outer and inner joint members 1,2 disappears. As a result, a certain amount of preload E is applied inthe axial direction to the torque transmitting balls 3, thus eliminatingthe rotation backlash (play in the circumferential direction).

Since the size of the clearance δ (=L−D_(BALL)) of the pocket in theaxial direction between the pocket 4 b of the cage 4 and the torquetransmitting balls 3 is set in a range of 0≦δ≦55μm, the constantvelocity universal joint of this embodiment has less resistance torotation when transmitting torque while taking an operating angle, andprovides good feel of steering (smoothness of rotation).

FIG. 32 shows a modification of the forth embodiment. In thisembodiment, the guide grooves 1 b of the outer joint member 1 and theguide grooves 2 b of the inner joint member 2 have regions 1 b 1, 2 b 1,respectively, that are free of undercut being provided thereon. Forexample, the region 1 b 1 is provided in the joint on the innermost sideof the center line O1 of the guide groove 1 b and is parallel to theaxis of the outer joint member 1. The region 2 b 1 is provided in thejoint on the opening side of the center line O2 of the guide groove 2 band is parallel to the axis of the inner joint member 2. By providingthe regions 1 b 1, 2 b 1 that are free of undercut, the operating angleof the joint can be increased.

FIG. 33 shows another modification of the forth embodiment. In thisembodiment, the entire region of the inner circumferential surface 4 aof the cage 4 is formed in a cylindrical surface, and the elastic member5 is mounted in the region 4 a 1 on the opening side of the innercircumferential surface 4 a while an auxiliary ring 7 is mounted in theinnermost side region 4 a 2′ of the inner circumferential surface 4 a.The auxiliary ring 7 is, for example, an integral ring that has claws 7b and spherical portions (or conical portions) 7 c similarly to theelastic member 5 described previously, and is fitted in the innermostside region 4 a 2′ and fastened by a retainer ring 8. The clearance S isprovided in the axial direction between the spherical surface (orconical surface) 7 c of the auxiliary ring 7 and the outercircumferential surface 2 a of the inner joint member 2. The clearance Sof the axial direction and the elastic member 5 constitute thepreloading means. This constitution has an advantage that theconfiguration of the cage 4 can be made simpler than in the embodimentdescribed above.

In the automotive steering apparatus shown in FIG. 34, a constantvelocity universal joint similar to those of the embodiments describedabove may be used as a universal joint (28) that connects the main shaft(21) and the intermediate shaft (22) while allowing it to make angulardisplacement freely.

By the forth embodiment, the following effects can be obtained.

(1) Since the preloading means is provided to reduce the clearancebetween the torque transmitting balls and the ball track, rotationbacklash (play in the circumferential direction) does not take place.

(2) Since the size of the clearance δ of the pocket in the axialdirection between the pocket of the cage and the torque transmittingballs is set in the range of 0≦δ≦55μm, the joint has less resistance torotation when transmitting torque while taking an operating angle, andprovides good feel of steering (smoothness of rotation).

(3) The operating angle of the joint can be increased by providing theregions free of undercut in the guide grooves of the outer joint memberand the inner joint member.

(4) It is made easier to assemble the cage into the outer joint memberby forming the region on the opening side of the inner circumferentialsurface of the outer joint member in a cylindrical surface that fitsonto the outer circumferential surface of the cage.

(5) The constant velocity universal joint of the present invention islight in weight, small in size and low cost, and rotates smoothlywithout backlash while being capable of taking a large operating angle,and therefore contributes to the improvements in performance such as thestability of steering, feel of steering, steering force andauto-centering capability, and in the freedom of designing the layout ofvehicle components when used in the steering apparatus of automobile.

What is claimed is:
 1. A ball fixed type constant velocity universaljoint comprising an outer joint member having a curved guide grooveformed in the axial direction on a spherical inner circumferentialsurface thereof, an inner joint member having a curved guide grooveformed in the axial direction on a spherical outer circumferentialsurface thereof, a ball disposed in a ball track formed by thecoordination of the guide groove of the outer joint member and the guidegroove of the inner joint member, and a cage that holds the ball, withthe center of the guide groove of the outer joint member and the centerof the guide groove of the inner joint member being offset to theopposite sides to each other by equal distances in the axial directionwith respect to the center plane of the joint that includes the centerof the ball, wherein the inner joint member is allowed to make relativedisplacement in the axial direction with respect to the cage, andelastic pressing means having a spherical surface that makes fittingcontact with the outer circumferential surface of the inner joint memberis interposed between the outer circumferential surface of the innerjoint member and the inner circumferential surface of the cage, so thatthe elastic force of the elastic pressing means presses the outercircumferential surface of the inner joint member to the side oppositeto the offset direction of the center of the guide groove thereof andwherein the inner joint member makes a relative displacement in theaxial direction opposite to the offset direction to elastically pressthe ball for applying a preload between the ball track and the ball. 2.The ball fixed type constant velocity universal joint as described inclaim 1, wherein said ball track has such a configuration that isreduced toward the opening of the joint, at least a region on theopening side of the inner circumferential surface of the cage is acylindrical surface that fits with the outer circumferential surface ofthe inner joint member, and said elastic pressing means is disposed onthe cylindrical surface.
 3. The ball fixed type constant velocityuniversal joint as described in claim 2, wherein the region on theopening side of said inner circumferential surface of the outer jointmember is a cylindrical surface that fits with the outer circumferentialsurface of the cage.
 4. The ball fixed type constant velocity universaljoint as described in claim 2 or 3, wherein the inner joint member and ashaft are formed as an integral part.
 5. A ball fixed type constantvelocity universal joint comprising an outer joint member having acurved guide groove formed in the axial direction on a spherical innercircumferential surface thereof, an inner joint member having a curvedguide groove formed in the axial direction on a spherical outercircumferential surface thereof, a ball disposed in a ball track formedby the coordination of the guide groove of the outer joint member andthe guide groove of the inner joint member, and a cage that holds theball, with the center of the guide groove of the outer joint member andthe center of the guide groove of the inner joint member being offset tothe opposite sides to each other by equal distances in the axialdirection with respect to the center plane of the joint that includesthe center of the ball, wherein: at least a region on the opening sideof the inner circumferential surface of said cage is formed in acylindrical surface that fits with the outer circumferential surface ofsaid inner joint member, and a retaining member having a sphericalportion that makes fitting contact with the outer circumferentialsurface of said inner joint member is disposed on the cylindricalsurface.
 6. The ball fixed type constant velocity universal joint asdescribed in claim 5, wherein the region on the opening side of saidinner circumferential surface of the outer joint member is a cylindricalsurface that fits with the outer circumferential surface of the cage. 7.The ball fixed type constant velocity universal joint as described inclaim 5 or 6, wherein the inner joint member and a shaft are formed asan integral part.